No abstract

Friedel-Crafts cyclization of 9 gave the diketone 10, which was converted into the dihydro compound 11 through a reduction-dehydration sequence. Dehydrogenation of 11 with p-chloranil in benzene provided the desired 12 as a green crystalline solid.Investigation of the electrochemical behavior of 12 by cyclic voltammetryl'Ol revealed two reversible reduction waves ( E Y d = -0.48 V, EYd = -1.07 V) and two irreversible oxidation waves (EF = 0.62 V, EF = 0.84 V). If we adopt the span of the oxidation and reduction potentials,as an experimental measure of the amphotericity of a molecule, diisopropyl-IDPL 12 may be considered a highly amphoteric hydrocarbon, I' 'I although ES,, = 1 . 1 0 V observed for 12 is slightly greater than that of PDPL (ES," = 0.99 V).I3] Interestingly, the EFm value (1.91 V for 12) is smaller than that of PDPL (2.19 V).13' This finding suggests substantial stabilities for both the doubly charged species 12'@ and 1220.Unexpectedly, treatment of the dihydro compound 11 with excess trityl tetrafluoroborate in dichloromethane afforded, instead of the mono-or dication salts, a radicalcation salt with nonstoichiometric composition, 12-(BF4)o,5 -o,61121 in 74% yield, which, on dissolution in concentrated D'SO,, gave the dication 12'@ as a dark blue solution. On the other hand, the dianion 12'@ could be generated as a bluish purple solution when 11 was treated with potassium mirror"3' under vacuum at -78 "C for a week. The 'H NMR chemical shifts for the three redox states 122@, 12, and 12'@ are compared in Table 1 .The most striking tropism at the central s-indacene and the terminal benzene rings, respectively. Currently, we are studying the intriguing solid-state properties of 12 and 12-(BF4)o,5 o , 6 .

B4tBu4 wurde durch Reduktion von tBuBF2 mit Na/K‐Legierung synthetisiert. Eine Röntgenstrukturanalyse ergab eine Tetrahedranstruktur (siehe Bild), deren B4C4‐Gerüst nur geringfügig vom idealen Tetraeder abweicht. Trotz gespannter B‐B‐Bindungen und relativ geringer sterischer Abschirmung des B4‐Gerüsts ‐ dieses ist größer als das C4‐Gerüst in C4tBu4 ‐ ist diese Organobor‐Verbindung erstaunlich inert.

A first indication of the occurrence of an organic derivative of diborane(2), HBBH, as intermediate is provided by the unexpected constitution of the structurally characterized product 1 of the reaction of (Me3Si)3CBCl2 with Na/K alloy. It may be assumed that (Me3Si)3C(Cl)BB(Cl)C(SiMe3)3 or (Me3Si)3CB: are initially formed and then react further to give the BB system. A stabilization by CH‐additions at the reactive double bonds would be the final step.

No abstract

Aus RBBr2 und Na/K‐Legierung erhält man ebenso wie zweistufig aus B4R4 und Na/K‐Legierung und nachfolgender Einwirkung von HCl das Tetraboran B4H2R4 (R = tBu). Aus NMR‐Daten und einer ab‐initio‐Rechnung für die Stammverbindung B4H6 sowie für B4H2Me4 läßt sich eine B4‐Tetraederstruktur 1 ableiten, in der zwei gegenüberliegende Kanten durch je ein H‐Atom überbrückt sind (D2d‐Symmetrie). Im Tetraboran B4H2R4 kann man mit Lithium in Tetrahydropyran (L) ein Brücken‐H‐Atom gegen die Gruppierung LiL2 austauschen. (L2Li)B4HR4 wurde durch Einkristall‐Röntgenstrukturanalyse charakterisiert.

Die Diazidoborane XB(N3)2 (1 a–d; X = tBu, Ph, (Me3Si)3C, C9H18N) und die Addukte von 1 a,b mit Triethylamin und Pyridin lassen sich aus den Dichlorboranen XBCl2 gewinnen.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.